here are some useful applets for the hobbiest. To use this correctly you need to know two initial parameters which are the beam diameter after it exits the crystal and the beam divergence without optics. Input into the top two boxes
http://www.lightmachinery.com/optical-calculations.php
the one I use is this.
http://www.lightmachinery.com/gausbeam.php
Link modified and made clickable
Timelord
http://www.lightmachinery.com/optical-calculations.php
the one I use is this.
http://www.lightmachinery.com/gausbeam.php
Link modified and made clickable
Timelord